i always get mine from forbidden planet, as there are two sites ( forbiddenplanet.co.uk and forbiddenplanet.com ) and i usuually find what im looking for. i noticed the dark avengers set is on the .com version, but says it's in on october the 15th. they do occasionally keep pushing stuff back, but it does come in sooner or later (my invaders took a couple of months to arrive, as do older sets and variants etc).
http://forbiddenplanet.com/40555-marvel-mi...engers-box-set/
your right though, collecting this kinda stuff from the uk is a pain. but the harder it is to get it, the more you'll enjoy it when it it arrives i find (either that or im insane...maybe, maybe...)
hope this helps!